In recent years, a cover glass (protective glass) has been frequently used to protect a display and to improve its appearance, on display devices having input functions such as mobile devices such as cell-phones and PDAs and touch panels.
Such a glass substrate for a display cover glass is required to be thin and to have high strength, and a glass substrate having increased strength by a chemical tempering method is commonly used.
Further, for such mobile devices and display devices with touch panels, hygiene management has been required.
To ticket vending machines at stations and ATMs used in the general public, and display devices with touch panels such as devices used in medical care facilities, due to their usage environment, various bacteria are very likely to be attached. Further, mobile devices also have the similar problem, since they are very frequently used although the users are limited.
Accordingly, for such devices and apparatus, it has been desired to impart antibacterial properties particularly to a glass substrate for a display cover glass which people very frequently touch.
In regard to this, glass excellent in antibacterial properties and also excellent in the strength is disclosed in JP-A-11-228186 (Patent Document 1). This document discloses that antibacterial properties and high strength (bending strength) can be imparted to glass by treating glass containing sodium with a molten salt of silver nitrate and potassium nitrate to replace sodium ions contained in glass with both of potassium ions and silver ions. Further, to provide glass also excellent in the transparency, it is considered preferable that the proportion (weight ratio) of a compound capable of donating M+ which replaces sodium ions of glass, to an antibacterial substance, is within a specific range.